tail: display file headers correctly with inotify

* src/tail.c (tail_forever_inotify): Use the fspec pointer to
distinguish previously output files, rather than a descriptor
from the inotify event.  That event descriptor was that of
the parent directory when files were created or renamed etc.
(check_fspec): Adjust for the new comparison.  Also show the
header when the file is truncated, since we show data
in this case also.
* tests/tail-2/F-headers.sh: A new test case.
* tests/local.mk: Reference the new test.
* NEWS: Mention the bug fix.

NEWS

@@ -56,6 +56,10 @@ GNU coreutils NEWS                                    -*- outline -*-
   tail --follow consistently outputs all data for a truncated file.
   [bug introduced in the beginning]
 
+  tail --follow=name correctly outputs headers for multiple files
+  when those files are being created or renamed.
+  [bug introduced in coreutils-7.5]
+
 ** New features
 
   chroot accepts the new --skip-chdir option to not change the working directory

src/tail.c

@@ -1046,7 +1046,9 @@ recheck (struct File_spec *f, bool blocking)
         {
           /* This happens when one iteration finds the file missing,
              then the preceding <dev,inode> pair is reused as the
-             file is recreated.  */
+             file is recreated.  Note this also means the file is redisplayed
+             in --follow=name mode if renamed away from and back to
+             a monitored name.  */
           new_file = true;
         }
       else
@@ -1321,7 +1323,7 @@ wd_comparator (const void *e1, const void *e2)
 
 /* Output (new) data for FSPEC->fd.  */
 static void
-check_fspec (struct File_spec *fspec, int wd, int *prev_wd)
+check_fspec (struct File_spec *fspec, struct File_spec **prev_fspec)
 {
   struct stat stats;
   char const *name;
@@ -1347,7 +1349,6 @@ check_fspec (struct File_spec *fspec, int wd, int *prev_wd)
   if (S_ISREG (fspec->mode) && stats.st_size < fspec->size)
     {
       error (0, 0, _("%s: file truncated"), name);
-      *prev_wd = wd;
       xlseek (fspec->fd, 0, SEEK_SET, name);
       fspec->size = 0;
     }
@@ -1355,11 +1356,11 @@ check_fspec (struct File_spec *fspec, int wd, int *prev_wd)
            && timespec_cmp (fspec->mtime, get_stat_mtime (&stats)) == 0)
     return;
 
-  if (wd != *prev_wd)
+  if (fspec != *prev_fspec)
     {
       if (print_headers)
         write_header (name);
-      *prev_wd = wd;
+      *prev_fspec = fspec;
     }
 
   uintmax_t bytes_read = dump_remainder (name, fspec->fd, COPY_TO_EOF);
@@ -1391,7 +1392,7 @@ tail_forever_inotify (int wd, struct File_spec *f, size_t n_files,
   bool found_unwatchable_dir = false;
   bool no_inotify_resources = false;
   bool writer_is_dead = false;
-  int prev_wd;
+  struct File_spec *prev_fspec;
   size_t evlen = 0;
   char *evbuf;
   size_t evbuf_off = 0;
@@ -1492,7 +1493,7 @@ tail_forever_inotify (int wd, struct File_spec *f, size_t n_files,
   if (follow_mode == Follow_descriptor && !found_watchable_file)
     return false;
 
-  prev_wd = f[n_files - 1].wd;
+  prev_fspec = &(f[n_files - 1]);
 
   /* Check files again.  New files or data can be available since last time we
      checked and before they are watched by inotify.  */
@@ -1524,7 +1525,7 @@ tail_forever_inotify (int wd, struct File_spec *f, size_t n_files,
             }
 
           /* check for new data.  */
-          check_fspec (&f[i], f[i].wd, &prev_wd);
+          check_fspec (&f[i], &prev_fspec);
         }
     }
 
@@ -1703,7 +1704,7 @@ tail_forever_inotify (int wd, struct File_spec *f, size_t n_files,
 
           continue;
         }
-      check_fspec (fspec, ev->wd, &prev_wd);
+      check_fspec (fspec, &prev_fspec);
     }
 }
 #endif
@@ -2316,7 +2317,8 @@ main (int argc, char **argv)
 
          FIXME-maybe: inotify has a watch descriptor per inode, and hence with
          our current hash implementation will only --follow data for one
-         of the names when multiple hardlinked files are specified.  */
+         of the names when multiple hardlinked files are specified, or
+         for one name when a name is specified multiple times.  */
       if (!disable_inotify && (tailable_stdin (F, n_files)
                                || any_remote_file (F, n_files)
                                || any_symlinks (F, n_files)

tests/local.mk

@@ -172,6 +172,7 @@ all_tests =					\
   tests/tail-2/inotify-hash-abuse2.sh		\
   tests/tail-2/F-vs-missing.sh			\
   tests/tail-2/F-vs-rename.sh			\
+  tests/tail-2/F-headers.sh			\
   tests/tail-2/descriptor-vs-rename.sh		\
   tests/tail-2/inotify-rotate.sh		\
   tests/tail-2/inotify-rotate-resources.sh	\

tests/tail-2/F-headers.sh

@@ -0,0 +1,59 @@
+#!/bin/sh
+# Ensure tail -F distinguishes output with the correct headers
+# Between coreutils 7.5 and 8.23 inclusive, 'tail -F ...' would
+# not output headers for or created/renamed files in certain cases.
+
+# Copyright (C) 2015 Free Software Foundation, Inc.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+. "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
+print_ver_ tail
+
+check_tail_output()
+{
+  local delay="$1"
+  grep "$tail_re" out ||
+    { sleep $delay; return 1; }
+}
+
+# Terminate any background tail process
+cleanup_() { kill $pid 2>/dev/null && wait $pid; }
+
+# Speedup the non inotify case
+fastpoll='-s.1 --max-unchanged-stats=1'
+
+for mode in '' '---disable-inotify'; do
+  rm -f a b out
+
+  tail $mode -F $fastpoll a b > out 2>&1 & pid=$!
+
+  # Wait up to 12.7s for tail to start.
+  tail_re="cannot open 'b'" retry_delay_ check_tail_output .1 7 ||
+    { cat out; fail=1; }
+
+  echo x > a
+  # Wait up to 12.7s for a's header to appear in the output:
+  tail_re='==> a <==' retry_delay_ check_tail_output .1 7 ||
+    { echo "$0: a: unexpected delay?"; cat out; fail=1; }
+
+  echo y > b
+  # Wait up to 12.7s for b's header to appear in the output:
+  tail_re='==> b <==' retry_delay_ check_tail_output .1 7 ||
+    { echo "$0: b: unexpected delay?"; cat out; fail=1; }
+
+  cleanup_
+done
+
+Exit $fail